How to secure Linux server

Step 1: Update you server regularly

apt install unattended-upgrades

Step 2: if you have Newer system, run the following

apt install apt-config-auto-update

if you have older try following

apt install update-notifier-common

Step 3: Configure the upgrades

sudo nano /etc/apt/apt.conf.d/50unattended-upgrades

Step 4. Activate the upgrades

dpkg-reconfigure — priority=low unattended-upgrades

Step 5: Configure the upgrade time

nano /lib/systemd/system/apt-daily.timer

Now, your system will upgrade automatically.

After two days you visit

/var/log/apt/history.log

And verify that updates has been done automatically
adduser sumit
usermod -aG sudo sumit
ssh-keygen -t ed25519
ssh-copy-id username@remote_host
https://www.youtube.com/watch?v=ZhMw53Ud2tY